Wind power and the use of wind turbines have gained increased attention as the quest for alternative energy sources continues. Wind power may be considered one of the cleanest, most environmentally friendly energy sources presently available. Different from traditional fossil fuel sources, wind power is completely renewable and does not produce noxious or environmentally harmful bi-products. With an increasing attention towards generating more energy from wind power, technological advances in the art have allowed for increased sizes of wind turbines and new designs of wind turbine components. However, as the physical sizes and availability of wind turbines increase, so does the need to balance the cost of manufacturing and operating wind turbines to further allow wind power to be cost-competitive with other energy sources.
A modern wind turbine typically includes a tower, generator a gearbox, a nacelle, and one more rotor blades. The rotor blades capture kinetic energy of wind using foil principles known in the art. The rotor blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
The size, shape, and weight of rotor blades are factors that contribute to energy efficiencies of wind turbines. However, size and shape produce opposite effects on efficiency an increase in rotor blade size increases the energy production of a wind turbine, while a decrease in weight also furthers the efficiency of a wind turbine. Furthermore, as rotor blade sizes grow, extra attention needs to be given to the structural integrity of the rotor blades. Presently, large commercial wind turbines are capable of generating between one and one-half megawatts to five megawatts of power. Some of the larger wind turbines have rotor blade assemblies larger than 90 meterse in diameter. Additionally, advances in rotor blade shape encourage the manufacture of a forward swept-shaped rotor blade having a general arcuate contour from the base to the tip of the blade, providing improved aerodynamics. Accordingly, efforts to increase rotor blade size, decrease rotor blade weight, and increase rotor blade strength, while also improving rotor blade aerodynamics, aid in the continuing growth of wind turbine technology and the adoption of wind energy as an alternative energy source.
The construction of a modern rotor blade includes a skin or shell, spar caps, and one or more shear webs. The skin, typically manufactured from layers of fiber composite and a lightweight core material, forms the exterior aerodynamic foil shape of the rotor blade. The spar caps provide increased rotor blade strength by integrating one or more structural elements running along the length of the rotor blade on both interior sides of the rotor blade. Shear webs are like a cross-beam or i-beam running essentially perpendicular to the top and bottom spar caps and extending across the interior portion of the rotor blade between the outer skins. Spar caps have typically been constructed from glass fiber reinforced composites, though some larger blades are beginning to include spar caps constructed from carbon fiber reinforced composites.
For swept-shaped rotor blades, the spar caps need to be constructed so as to have a general contour following the curvature of the rotor blade. However, a problem with the current state of the art is that the spar caps made from composites of fibrous materials wrinkle or bunch around the inside curve when formed into a swept shape.
For larger rotor blades, regardless of their shape, problems exist in creating the spar caps that are strong enough without adding excessive weight to the rotor blades. Further, the larger the rotor blade the larger the spar cap is, and therefore, the transportation of the spar caps from the place of manufacture to the assembly location becomes increasingly difficult with size.
There is a desire, therefore, to form a swept-shaped spar cap that maintains the strength and structural integrity of fiber material without creating wrinkles or bunches in the fibers. There is a further desire to construct spar caps, regardless of shape, in a manner that promotes easier and lower-cost transportation, considering the size of an assembled spar cap.